This invention relates to a magnetron-discharge-enhanced dry process apparatus.
A description of prior art dry process apparatus of this type is set forth in the Japanese Journal of Applied Physics, Vol. 20, No. 11, 1981, pp. L 817-820, and Extended Abstracts of the 18th Conference on Solid State Devices and Materials, Tokyo, 1986, pp. 495-498.
Schematic diagrams of the apparatus described in these papers are shown in FIGS. 1A and 1B. In FIG. 1A the material to be processed is situated on the cathode; in FIG. 1B it is situated on the anode.
The apparatus in FIG. 1A comprises a reactor 10 with an etching gas inlet 12 and an outlet 14 leading to a vacuum pump. In this example of the prior art, part of the floor of the reactor 10 is a cathode 18 which is fitted to a nonconductive section 16 made of a dielectric material such as Teflon. The material to be etched (which is hereinafter assumed to be a substrate) 20 is placed onto the cathode 18. Outside the reactor 10, located beneath the substrate 20 to be etched and parallel to it, is a permanent magnet assembly 22 that presents in sequence N-, S-, and N- poles toward the substrate. This permanent magnet assembly 22 is scanned (moved) in a reciprocating horizontal motion (represented by the arrows marked a in the drawing) parallel to the substrate 20. A high-frequency (rf) oscillator 24 (including a power supply and having an oscillation frequency of 13.56 MHz) supplies electromagnetic waves to the cathode 18.
After the material (substrate) 20 to be etched is placed onto the cathode 18 in the reactor 10, the reactor 10 is evacuated by the vacuum pump and etching gas is introduced at a pressure of 10.sup.-2 to 10.sup.-3 Torr; then electromagnetic waves are applied to the cathode 18 by the rf oscillator 24, thereby ionizing the etching gas to create a plasma of positive ions and negative electrons. The supplied electromagnetic waves generate an alternating electric field E oriented perpendicularly to the cathode 18. The permanent magnet assembly 22 generates a magnetic field B parallel to the cathode 18 in the positions between the N- and S-poles. Intersecting orthogonally in the space above the substrate 20, the alternating electric field E and magnetic field B cause the lightweight electrons to spiral along the lines of magnetic force in a tight cyclotron motion during which they undergo high-energy collisions with the neutral etching gas, thereby generating a high-density plasma which induces a magnetron discharge 26 in this region.
The apparatus of the prior art shown in FIG. 1B comprises a reactor 10 from which air can be evacuated, an anode 17 to which is secured a vapor-deposition substrate 20 on which vapor is to be deposited, a cathode 18 connected to an rf oscillator 24 (with a frequency of 13.56 MHz), a permanent magnet assembly 22 for inducing a magnetron discharge, a heater 19 for heating the vapor-deposition substrate 20, and a reactant gas 21 for the vapor-deposition of a thin film. The apparatus deposits a film of a material such as aluminum on the substrate 20 as follows. First the reactor 10 is evacuated by means of a pump; then a reactant gas 21 is introduced at a pressure of 2.3 Torr, and 13.56 MHz high-frequency power is applied to the cathode 18 from the rf oscillator 24, ionizing the reactant gas 21 to create a plasma of positive ions and negative electrons. The applied electromagnetic waves also generate an alternating electric field oriented perpendicularly to the anode 17, while the permanent magnet assembly 22, which comprises two bar magnets, creates a magnetic field parallel to the anode in the position between the N and S magnetic poles. Intersecting orthogonally in the space above the substrate 20, the alternating electric field E and magnetic field B cause the lighweight electrons to spiral along the lines of magnetic force in a tight cyclotron motion during which they undergo high-energy collisions with the neutral etching gas 21, thereby generating a high-density plasma which induces a magnetron discharge.
The ionization rate of a normal rf discharge of the etching gas or reactant gas is only about 10.sup.-4. The ionization rate of a magnetron discharge is about 10.sup.-2, at least two orders of magnitude better, and the etch rate is improved by at least one order of magnitude. Moreover, there is improvement in both the deposition rate and the quality of the resulting film.
A problem in the prior art as shown in FIG. 1A is that the magnetic field B created above the material to be etched (e.g. the substrate 20) is nonuniform. Uniform substrate etching can be achieved only by scanning (reciprocating) the permanent magnet assembly 22 horizontally back and forth with respect to the substrate surface, but when permanent magnet assembly 22 is scanned horizontally, the magnetron discharge 26 also moves horizontally and this motion reduces the mean etch rate.
In an effort to overcome this problem two independent magnets have been used with the N-pole of one magnet facing the S-pole of the other inside the reactor. Although a uniform magnetic field can be produced in this way between the magnets, great skill and effort are demanded, and the extra space required to mount two magnets inside the reactor is hardly an advantage from the point of view of apparatus structure.
A similar problem arises in the prior art shown in FIG. 1B. The use of a pair of bar magnets in the permanent magnet assembly 22 creates a nonuniform magnetic field over the substrate 20, and vapor cannot be deposited uniformly on the substrate unless the permanent magnet assembly 22 is rotated in the horizontal plane. The pair of bar magnets in the permanent magnet assembly 22 also take up considerable space, making a compact apparatus configuration difficult to achieve.